Chromate surface treated steel sheet

Abstract

A chromate surface treated steel sheet having very excellent paintability, corrosion resistance, and workability, more specifically surface treated steel sheets for paint coating, having very excellent properties, specifically with respect to corrosion resistance after paint coating, paint adhesion in services long after the paint coating (so-called secondary paint adhesion), corrosion resistance of paint coating defect portions, and resistance to secondary work cracking. The steel sheet contains not more than 0.15% carbon, 0.005 to 0.10% acid soluble aluminium, 0.5 to 20% chromium with the balance being iron and unavoidable impurities, and the chromate coating applied on the steel substrate comprises a metallic chromium layer in an amount ranging from 1 to 300 mg/m2, and a hydrated chromium oxide layer in an amount ranging from 5 to 50 mg/m2 in term of the metallic chromium contained therein.

What is claimed is: 
     
       1. A chromate surface-treated steel sheet, excellent in paintability, corrosion resistance and workability comprising a chromium-containing steel substrate containing not more than 0.15% carbon, 0.005 to 0.10% acid soluble aluminium, 0.5 to 20% chromium with the balance being iron and unavoidable impurities, and a chromate coating applied on said steel substrate, said coating comprising a metallic chromium layer in an amount ranging from 1 to 300 mg/m 2 , and a hydrated chromium oxide layer in an amount ranging from 5 to 50 mg/m 2  in term of the metallic chromium contained therein. 
     
     
       2. A steel sheet according to claim 1, wherein said steel substrate contains not more than 0.02% carbon. 
     
     
       3. A steel sheet according to claim 1, wherein said steel substrate further contains 0.1 to 10% nickel. 
     
     
       4. A steel sheet according to claim 1, wherein said steel substrate contains not more than 0.02% carbon and 0.1 to 10% nickel. 
     
     
       5. A steel sheet according to claim 1, wherein said steel substrate further contains not more than 0.0030% boron. 
     
     
       6. A steel sheet according to claim 5, wherein said steel substrate further contains 0.1 to 10% nickel. 
     
     
       7. A steel according to claim 1, wherein said steel substrate further contains at least one member selected from the group consisting of Ti, Nb, Zr, and V in an amount ranging from 0.03 to 0.5%. 
     
     
       8. A steel sheet according to claim 7, wherein said steel substrate contains not more than 0.02% carbon and 0.1 to 10% nickel.